Hybrid vehicles typically have a combustion engine and an eMachine which can act as both an electric motor and a generator. During braking, such vehicles are capable of capturing and storing the braking energy in a battery for later use in propelling the vehicle. This process is commonly referred to as regenerative braking. Some hybrid vehicles are configured to use the energy stored in the battery to boost propulsion performance beyond the capabilities of the engine acting alone. However, it is generally preferred to instead operate the vehicle in a manner which simulates the propulsion response of the engine only. This assures the operator will experience a response which is consistent with non-hybrid vehicles.
In order to achieve this engine-only simulated response when using both the electric motor and engine to propel the vehicle, many hybrid vehicles reduce the output of the engine by that of the hybrid motor to match the equivalent engine-only output. This method is typically satisfactory for normally aspirated engines, since the torque produced by the engine at a given rotational engine speed (rpm) is relatively constant over time.
In turbocharged engines, however, the power generated by the engine may change with time due to the effect of the turbocharger. A turbocharger uses engine exhaust gases to drive a turbine wheel. A shaft connects the turbine wheel to a compressor wheel in the air intake path of the engine. Therefore, as the turbine wheel is driven by the flow of exhaust gas, the compressor wheel also spins and compresses the air to the intake of the engine. As the intake air is compressed over time (and increasing amounts of fuel are added), the power generated by the engine also increases. As the engine output increases and more exhaust gases are generated, the turbine and compressor wheels spin faster, thereby increasing the power generated by the engine still further. However, because the turbocharger requires time to overcome the inertia of the compressor wheel and begin to spin, there is a delay in the delivered power response. This effect is commonly referred to as turbo lag and gives the operator a feeling of gradual building of engine power.
The turbocharger effect prevents the simple substitution of electrical power for engine power in a hybrid vehicle where an engine-only equivalent response is desired. This is because as electrical power from the motor replaces engine power, the engine power generation capacity is diminished even further due to the loss of the turbo effect. In other words, if a portion of the engine power is substituted by power generated by the electric motor, the resulting combination output will not match that of the equivalent output if the engine had been acting alone.
Thus, there is a need for improvement in this field.